This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 2003-086166 filed in Japan on Mar. 26, 2003, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a novel adamantanetricarboxylic acid derivative which is useful for the formation of a film of a polybenzazole (imidazole, oxazole or thiazole) having high heat resistance and a low dielectric constant.
2. Description of the Related Art
Polybenzazoles having an adamantane skeleton are useful as highly heat resistant resins (Journal of Polymer Science, Part A-1 (1970), 8(12), p. 3665-3666). In particular, highly crosslinked polybenzazoles using a trifunctional adamantane derivative involve a multitude of molecular-scale voids, have a low relative dielectric constant and satisfactory mechanical strength and heat resistance and are thereby very useful as materials for interlayer dielectrics (Japanese Unexamined Patent Application Publication (JP-A) No. 2001-332543). These highly crosslinked polybenzazoles can be prepared, for example, by heating a material in the presence of a condensing agent such as a polyphosphoric acid. However, the resulting highly crosslinked resin is hardly soluble in solvent and cannot be significantly applied to a substrate by coating, thus a film having a sufficient thickness necessary as an interlayer dielectric cannot be significantly formed.
A thin film of a wholly aromatic chain polybenzazole is formed by a method in which an aldehyde derivative as a material monomer is spread over an aqueous solution of an amine as another material monomer to form a film by polymerization on a gas-liquid interface; the film is laminated on a substrate by a horizontal attachment method and is subjected to a thermal treatment in the air to form a thin film of a polybenzazole (Japanese Unexamined Patent Application Publication (JP-A) No. 62-183881). However, the method is not suitable for industrial production, since it takes quite a long time to form the thin film. In addition, the precursor polyimine is subjected to an oxidative thermal treatment in a final process, and the resulting polybenzazole film may be possibly oxidized, thus a lower dielectric constant as a dielectric film is not expected.
In addition, adamantanepolycarboxylic acid derivatives used as a material monomer have a significantly high polarity as a compound and are soluble in quite limited types of solvents. In particular, these monomers are hardly soluble in a solvent having a relatively low polarity, and a film having a thickness of several hundreds nanometers required as an interlayer dielectric for a semiconductor device cannot significantly be formed. Thus, dielectric films of highly crosslinked polybenzazoles using a trifunctional adamantane derivative have been hardly formed.